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CFL Number in Comsol 4.1 ?

Posted Mar 21, 2011, 8:27 a.m. EDT 6 Replies

Alois Pfenniger
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Hi,

Is there somebody who can tell me what is the new variable name for the CFL number in Comsol 4.1? It used to be dt_cfl_gn_app in 3.5a, e.g. dt_cfl_g1_ns for geometry 1 and application mode ns (Navier-Stokes). I cannot find the new name in the documentation of Comsol 4.1, but it must have changed, since I get an error message when I try the old variable name...

Thanks a lot.

Alois Pfenniger
6 Replies Last Post Apr 4, 2011, 5:13 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 23, 2011, 2:44 a.m. EDT
Hi

I have also looked for it, but I cannot find the name in v4, you will have to ask support ;)

--
Good luck
Ivar
Hi I have also looked for it, but I cannot find the name in v4, you will have to ask support ;) -- Good luck Ivar
Certified Consultant
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Posted: 1 decade ago Mar 28, 2011, 11:50 a.m. EDT
Hello,
the CFL number that was available earlier was a replacement for the automatic time stepping. In the current version of the flow equations the CFL number is obsolete, and since it can only be cumputed during solution, and not as a postprocessing variable, it was not included in the current version of COMSOL.

A CFL number can still be constructed using the variable "timestep". It is only avaliable during solution and represents the time step taken by the solver.
--
Niklas
Hello, the CFL number that was available earlier was a replacement for the automatic time stepping. In the current version of the flow equations the CFL number is obsolete, and since it can only be cumputed during solution, and not as a postprocessing variable, it was not included in the current version of COMSOL. A CFL number can still be constructed using the variable "timestep". It is only avaliable during solution and represents the time step taken by the solver. -- Niklas
Alois Pfenniger
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Posted: 1 decade ago Mar 30, 2011, 8:07 a.m. EDT
Hi,

thanks Niklas for commenting on this issue. Actually I followed the suggestion by Ivar and contacted the support.

Here is what I got:

Concerning the "Pseudo time stepping for stationary equation form", the CFL variable name is "spf.cflloc"

Concerning the time stepping for the time dependent solver, as mentionned by Niklas, the CFL based time step variable has been removed since now automatic time stepping is available. A CFL based time step can still be constructed in version 4, using a global integration coupling variable.

Alois

Hi, thanks Niklas for commenting on this issue. Actually I followed the suggestion by Ivar and contacted the support. Here is what I got: Concerning the "Pseudo time stepping for stationary equation form", the CFL variable name is "spf.cflloc" Concerning the time stepping for the time dependent solver, as mentionned by Niklas, the CFL based time step variable has been removed since now automatic time stepping is available. A CFL based time step can still be constructed in version 4, using a global integration coupling variable. Alois
Danial Tz
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Posted: 1 decade ago Mar 30, 2011, 4:24 p.m. EDT

automatic time stepping


Hi Alois,

what is this automatic time stepping? I could not find any documentation about it (except very general overview)

I want to mention in my paper that I have respected the CFL, but i don't have a reference. I thought the solver was using like <100 CFL or something like that.

Danial



--
Comsol 4.1
Ubuntu 10.04.1
[QUOTE] automatic time stepping [/QUOTE] Hi Alois, what is this automatic time stepping? I could not find any documentation about it (except very general overview) I want to mention in my paper that I have respected the CFL, but i don't have a reference. I thought the solver was using like
Alois Pfenniger
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Posted: 1 decade ago Mar 31, 2011, 3:32 a.m. EDT
Hi Danial,

I was asking myself the same question... which I then asked to Comsol support. Here is what I got:

My question:
I do not see where I can select automatic time stepping for the generalised alpha time dependent solver. I only have
"free", "strict", "intermediate", "manual" as possible options. Where can I select "automatic" time stepping?

Comsol support answer:
There is no setting named "automatic" for the time steps. As you have noticed there are "free", "strict" and "intermediate". Look at the (dynamic) help menu and you will understand that in all three methods time steps are taken automatically to a certain extend.

I cannot tell you more unfortunately...

Alois
Hi Danial, I was asking myself the same question... which I then asked to Comsol support. Here is what I got: My question: I do not see where I can select automatic time stepping for the generalised alpha time dependent solver. I only have "free", "strict", "intermediate", "manual" as possible options. Where can I select "automatic" time stepping? Comsol support answer: There is no setting named "automatic" for the time steps. As you have noticed there are "free", "strict" and "intermediate". Look at the (dynamic) help menu and you will understand that in all three methods time steps are taken automatically to a certain extend. I cannot tell you more unfortunately... Alois
Danial Tz
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Posted: 1 decade ago Apr 4, 2011, 5:13 a.m. EDT

Hi Danial,

I was asking myself the same question... which I then asked to Comsol support. Here is what I got:

My question:
I do not see where I can select automatic time stepping for the generalised alpha time dependent solver. I only have
"free", "strict", "intermediate", "manual" as possible options. Where can I select "automatic" time stepping?

Comsol support answer:
There is no setting named "automatic" for the time steps. As you have noticed there are "free", "strict" and "intermediate". Look at the (dynamic) help menu and you will understand that in all three methods time steps are taken automatically to a certain extend.

I cannot tell you more unfortunately...

Alois


Yes, anything other than manual is automatic in Comsol. Nevertheless, there is close to no documentation about the internals of it.

Danial


--
Comsol 4.1
Ubuntu 10.04.1
[QUOTE] Hi Danial, I was asking myself the same question... which I then asked to Comsol support. Here is what I got: My question: I do not see where I can select automatic time stepping for the generalised alpha time dependent solver. I only have "free", "strict", "intermediate", "manual" as possible options. Where can I select "automatic" time stepping? Comsol support answer: There is no setting named "automatic" for the time steps. As you have noticed there are "free", "strict" and "intermediate". Look at the (dynamic) help menu and you will understand that in all three methods time steps are taken automatically to a certain extend. I cannot tell you more unfortunately... Alois [/QUOTE] Yes, anything other than manual is automatic in Comsol. Nevertheless, there is close to no documentation about the internals of it. Danial -- Comsol 4.1 Ubuntu 10.04.1

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